1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly, to the semiconductor device and the manufacturing method thereof for a complementary metal oxide semiconductor (herein abbreviated as CMOS) image sensor.
2. Description of the Prior Art
As the development of electronic products such as digital cameras and scanners progresses, the demand for image sensors increases accordingly. In general, image sensors in common usage nowadays are divided into two main categories: charge coupled device (CCD) sensors and CMOS image sensors (CIS). Primarily, CMOS image sensors have certain advantages of low operating voltage, low power consumption, and ability for random access. Furthermore, CMOS image sensors are currently capable of integration with the semiconductor fabrication process. Based on those benefits, the application of CMOS image sensors has increased significantly.
The CMOS image sensor separates incident light into a combination of light of different wavelengths. For example, the CMOS image sensor can consider incident light as a combination of red, blue, and green light. The light of different wavelengths is received by respective photosensitive elements such as photodiodes disposed in the substrate and is subsequently transformed into digital signals of different intensities. Thus, it is conceivable, that the substrate, particularly at where the photosensitive elements (that is the pixel region) are formed, should be protected from any contamination. For example, in order to prevent metal contamination, salicides are avoided from forming in the pixel region in the prior art. However, it results that the pixel region suffers high contact resistances and signal transmission is adversely impacted.
Therefore, semiconductor devices and manufacturing method for reducing resistance in the pixel region without causing metal contamination is still in need.